26 ILLIXOIS BIOLOGICAL MOXOGRAPHS [26 



PART II 



THE EFFECT OF SUCCESSIVE REMOVAL UPON THE RATE 

 AND COMPLETENESS OF REGENERATION 



One of the most ioteresting facts in connection with regeneration 

 is the ability to replace a part after repeated removal. The present set 

 of experiments was made in continuation of jarevious studies of the 

 effect of successive removal upon the rate of regeneration (Zeleny 1907, 

 1908, 1909). The earlier studies show that as a rule the rate of regen- 

 eration following a first removal is no greater than that following second 

 and latei^reuiovals if the effect of age is eliminated. Where a difference 

 exists it seems to be in favor of the later regenerations. 



The matter is of very great interest in connection with general 

 problems of development and particularly in connection with 'the ques- 

 tion as to the existence or non-existence of a necessary limit to the 

 amount of living substance that a single individual may produce during 

 its life cycle. Does the production of a group of tissues use up a part 

 of a certain store of developmental energy or of developmental factors 

 possessed by the individual or is this store inexhaiistible or perchance 

 even increased by exercise of the functioia? These questions warrant 

 more extended study especially in view of the additional analysis that 

 has been made of other factors controlling the rate of regeneration. 

 The paper includes all the unpublished data that have been obtained 

 on the problem at hand. In general these data support the conclusions 

 previously reached. The descriptions of the individual experiments 

 will first be given and they will be followed bj- a discussion of the general 

 results. 



Experiment I Rana clamitans Skries 3628-3675 

 Material and Method The tadpoles were collected on December 9, 

 1911. At the time of the operation on December 20 the average total 

 length Avas 33.0 mm. and the average tail length 21.6 mm. Forty-eight 

 individuals were divided into twelve sets of four each. The four indi- 

 viduals of a set are called a, h, c, and d. Approximately one-half in 

 length of the tail was removed by a transverse cut in c and d. After 

 21 days the regenerated portion of the tail was removed. In individual 

 c the second cut came inside of the border liue between old and new 



